The reason for the increased interest in gypsum is two-fold. First, we just don't get as much sulfur from rainfall as was the case 20 years ago. Sulfur deficiency is becoming more common in areas where it was once nearly non-existent. Gypsum is a reasonably priced source of sulfur. Second, the installation of "scrubbers" at coal-fired powered plants has resulted in a high quality gypsum byproduct called FGD (flue gas desulfurized) gypsum, which is marketed as Gypsoil.

Although gypsum is a good calcium source, the vast majority of local soils have little need for additions of this nutrient. After all, we live and work on a mountain of limestone. If we're flush with anything in east central Wisconsin, it's calcium.

Further, calcium does not leach from the soil to a great extent because it is a positively charged ion. Hence, increasing calcium levels in the soil is generally not a good primary reason to apply gypsum. Gypsum, unlike lime, has no effect on soil pH.

Gypsum is also a good source of sulfur, a nutrient that behaves similar to nitrogen in that it leaches from the plant root profile. One ton of gypsum will provide 300-360 pounds of sulfur per acre at a comparatively low cost per pound of nutrient. Of course, not all of this sulfur will be used before it moves deeper in the soil profile.

Gypsum's impact on soil quality is a topic currently on the debate floor as research results are highly variable. Improved water infiltration, reduced compaction, deeper rooting, and enhanced biological activity have all been claimed attributes of gypsum.

We do know that using gypsum to "balance" the Ca:Mg ratio has no economic or scientific basis. It's been proven a non-factor over and over again in research trials, although some marketers continue to tout its merit. Most Wisconsin research has not consistently shown benefits from gypsum applications beyond the expected nutritional additions. Some studies from other states have shown soil quality benefits.

If you plan to use gypsum, it's suggested that untreated check strips be left to evaluate effectiveness. I would be interested in knowing about or seeing any field observations.

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Gypsum valuable as nutritional supplement

There seems to be a lot of interest over the past year in applying gypsum to farm fields. Gypsum (calcium sulfate dihydrate) contains about 23 percent calcium and 18 percent sulfur in its purest form.

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